Mirror assembly and optical assembly with hydrogen barrier

Abstract

The present invention relates to a mirror assembly (30) comprising: a substrate (31) having a front side (31a) and a back side (31b), the front side (31a) having a mirror surface (32a) for reflecting radiation (5) and the back side (31b) facing away from the front side (31a); and at least one actuator (27) for generating deformation of the mirror surface (32a). The at least one actuator (27) is fixed to the back side (31b) of the substrate (31), and the mirror assembly (30) has a hydrogen barrier (38) designed to protect hydrogen-sensitive material (M) on the back side (31b) of the substrate (31)—particularly on the at least one actuator (27)—from hydrogen from the environment of the mirror assembly (30). The invention also relates to optical assemblies, particularly EUV lithography apparatuses (1), which include mirror assemblies (30) of this type.

Description

[0001] Cross-references to related applications

[0002] This patent application claims priority to German patent application DE 10 2019 213 349.5, filed on September 3, 2019, the entire contents of which are incorporated herein by reference. Background of the Invention

[0004] This invention relates to a mirror arrangement comprising: a substrate including a front side having a mirror surface for reflecting radiation and a back side opposite to the front side; and one or more actuators in the form of actuator assemblies, for example, for generating deformation of the mirror surface. The invention also relates to an optical arrangement, particularly an EUV lithography apparatus, having at least one such mirror arrangement.

[0005] The aforementioned mirror arrangement allows for targeted (local) deformation of the mirror surface formed on the front side of the substrate via an actuator. For example, the purpose of deforming the mirror surface can be to specifically correct aberrations in the EUV lithography equipment in which the mirror arrangement is set.

[0006] US 5,986,795 describes a deformable mirror for EUV radiation, wherein an actuator is disposed between a front plate and a reaction plate forming the back of the mirror and coupled to both plates to induce deformation on the mirror surface of the deformable mirror.

[0007] For example, in optical arrangements such as (EUV) lithography units, it may be necessary to permanently or, for example, mix hydrogen into the environment surrounding the mirror arrangement during cleaning cycles. In this case, hydrogen can exist entirely in excited states: as molecules (H2), as atoms, as excited molecules or atoms, or as hydrogen ions. The presence of EUV radiation promotes the existence of hydrogen in different excited states. Many materials are damaged by hydrogen attack and are therefore hydrogen-sensitive materials. Therefore, it is necessary to select materials that are stable against hydrogen attack or to protect hydrogen-sensitive materials from hydrogen attack.

[0008] Purpose of the invention

[0009] The object of the present invention is to provide a mirror arrangement and an optical arrangement having at least one such mirror arrangement, wherein hydrogen-sensitive materials are effectively protected from hydrogen attack. Summary of the Invention

[0010] This objective is achieved by a mirror arrangement of the type described above, wherein at least one actuator is fixed to the back side of the substrate, and wherein the mirror arrangement includes a hydrogen barrier configured to protect the hydrogen-sensitive material on the back side of the substrate, particularly the hydrogen-sensitive material on at least one actuator, from hydrogen attack from the environment surrounding the mirror arrangement.

[0011] This invention proposes fixing actuators to the back side of a substrate, and protecting them—along with any other hydrogen-sensitive materials present on the back side of the substrate—from the hydrogen in the environment surrounding the mirror arrangement by hydrogen barriers. The hydrogen-sensitive materials can be, for example, the actuator itself or its housing, insulation layer, conductor cable / conductor track, etc., mounted on the back side of the substrate. If the substrate is exposed on the back side and if the substrate is made of hydrogen-sensitive material, the substrate itself can also be protected from hydrogen attack by hydrogen barriers.

[0012] Actuators can be fixed in a regular arrangement or grid (actuator array) on the back side of the substrate, but in principle any desired arrangement of actuators on the back side of the substrate is possible. Generally, adjacent actuators or adjacent groups of interconnected actuators (actuator assemblies) are not directly adjacent to each other on the back side of the substrate, but are spaced apart from each other; in other words, there are gaps or gaps between pairs of adjacent actuators or actuator assemblies.

[0013] In one embodiment, at least one actuator is secured to the back side of the substrate by an adhesive layer, the exposed surface area of ​​which is at least partially, and particularly completely, protected from hydrogen attack by a hydrogen barrier. In this case, the actuator is adhered to the substrate directly or indirectly (i.e., through one or more intermediate layers on the back side of the substrate). Typically, continuous adhesive layers are used to secure the actuators, meaning that the adhesive layers also extend into the gaps between adjacent actuators and / or between multiple groups of interconnected actuators.

[0014] The surface area of ​​the adhesive layer exposed to the surrounding environment can be formed, for example, in the gaps between actuators. In the gap area, the adhesive layer can be thicker than in the area between the corresponding actuator and the back of the substrate, but it can also be applied thin enough that it is not thicker in the gap or gap between actuators than in the area where the actuator is connected to the substrate or intermediate layer.

[0015] In one development, the hydrogen barrier forms a water vapor diffusion barrier to protect the adhesive layer from water vapor. In this case, the hydrogen barrier additionally functions as a water vapor diffusion barrier to further protect the adhesive layer from moisture penetration. Because hydrogen molecules are smaller than water vapor molecules, the requirements for the materials forming the hydrogen barrier are generally more stringent than those for the water vapor diffusion barrier. Therefore, materials suitable for hydrogen barriers are usually also suitable for water vapor diffusion barriers, but the reverse is not always true.

[0016] Moisture penetration or changes in humidity in the surrounding environment of the mirror arrangement are particularly problematic for the adhesive layer or other organic materials mechanically connected to the mirror. This is because if the adhesive layer absorbs moisture from the environment, it expands, and stress may be introduced into the adhesive layer or organic material. This stress in the adhesive layer or organic material is typically transmitted to the substrate, thus subjecting it to stress, which can lead to drift—an undesirable change in the deformation on the mirror surface over time. Aberrations also exist in the beam path of the optical arrangement due to moisture variations. Moisture penetration into the adhesive layer or organic material is particularly prevalent in areas where the adhesive is exposed or where the organic material is located; therefore, it is advantageous if hydrogen barriers are used as water vapor diffusion barriers, at least in the exposed areas. It should be understood that hydrogen barriers can be formed not only in these exposed surface areas but also in areas where the actuator is applied to the back of the substrate.

[0017] In another development, the surface of the hydrogen barrier facing the surrounding environment is hydrophobic and / or the hydrogen barrier includes at least one hydrophobic material. If the surface of the hydrogen barrier facing the surrounding environment is hydrophobic, the absorption of moisture can be reduced. The material on the top side of the hydrogen barrier can be made hydrophobic, for example, by surface treatment, such as by plasma treatment, and / or by irradiation with UV radiation (optionally pulsed), by coating, or by surface termination. The hydrogen barrier itself may also include at least one hydrophobic material to counteract the permeation of water vapor, thereby forming a water vapor diffusion barrier.

[0018] In another embodiment, the hydrogen diffusion coefficient of the hydrogen barrier is less than 5 x 10⁻⁶. -14 m 2 / s, preferably less than 1x10 -17 m 2 / s, more preferably less than 1x10 -21 m 2 / s. To ensure maximum protection of hydrogen-sensitive materials, the hydrogen barrier should allow as little hydrogen as possible to pass through it. To achieve this, the hydrogen barrier is constructed of layers, materials, and / or combinations of materials with hydrogen diffusion coefficients lower than the aforementioned values. Examples of hydrogen diffusion coefficients for many materials are given below: Ru: 4 × 10⁻⁶-14 m 2 / s, Al: 1×10 -14 m 2 / s, Al2O3: 10 -23 m 2 / s (amorphous) or 10 -28 m 2 / s (crystal). The hydrogen diffusion coefficient here is usually based on standard conditions (1 atm, 25 °C).

[0019] In another embodiment, the hydrogen barrier comprises at least one material and / or combination of materials having a lower solubility for hydrogen than the hydrogen-sensitive material (M). Solubility is defined as hydrogen at atmospheric pressure and refers to the volume (in cubic centimeters) of (molecular) hydrogen absorbed by 100 grams of the hydrogen-absorbing material. For details on this definition, please refer to the article “A Theoretical Formula for the Solubility of the Hydrogens in Metals” cited in US2016 / 0187543 A1, RHFowler et al., Proc.R.Soc.Lond.A 160, page 37ff, (1937), the entire contents of which are incorporated herein by reference. The lower solubility for hydrogen can counteract the brittleness of the hydrogen barrier material. In this way, the lifespan of the mirror arrangement or its hydrogen-sensitive material and / or components can be extended, meaning they do not require frequent replacement. Furthermore, it is advantageous that the hydrogen barrier material or combination of materials is selected such that it does not form any gaseous hydrogen compounds.

[0020] In one embodiment, the hydrogen barrier comprises at least one material in the form of an oxygen-containing compound having a formation enthalpy (Gibbs energy) of less than -400 kJ / mol O2 under standard conditions, preferably less than -800 kJ / mol O2, and more preferably less than -1000 kJ / mol O2.

[0021] In another embodiment, the hydrogen barrier comprises at least one material in the form of a nitrogen-containing compound having a formation free enthalpy (Gibbs energy) of less than -200 kJ / mol N2 under standard conditions, preferably less than -350 kJ / mol N2, and more preferably less than -600 kJ / mol N2.

[0022] Compounds with particularly high enthalpy of formation are generally chemically inert to hydrogen attack, making them ideal materials for hydrogen barriers. When selecting materials, the enthalpy of formation of the corresponding oxide or nitride compound can be compared to the associated hydrides produced by the chemical reaction of the corresponding material—e.g., a metallic material—with hydrogen. The enthalpy of formation of the corresponding compound (or the amount of enthalpy of formation) should be greater than that of the corresponding hydride compound. The enthalpy of formation G takes into account the fact that the reaction with hydrogen produces gaseous reaction products; however, the enthalpy of formation H used as a criterion for material selection in WO 2013 / 124224 A1 does not take this into account. In the case of forming gaseous reaction products, the enthalpy of formation H of the material can be lower, but it may still react with hydrogen due to the increase in entropy.

[0023] In one embodiment, the hydrogen barrier comprises at least one metal oxide, preferably selected from the group consisting of Al₂O₃, MgO, CaO, La₂O₃, TiO₂, ZrO₂, Ta₂O₅, Al₂O₃, Y₂O₃, Ce₂O₃, and compounds thereof. Al₂O₃ has a Gibbs energy of approximately -1050 kJ / mol O₂ under standard conditions. The other metal oxides also have high enthalpies of formation and are therefore largely chemically inert to hydrogen attack.

[0024] In another embodiment, the hydrogen barrier comprises at least one material selected from the group consisting of Al, Au, Ag, Zn, Mo, Si, W, Ti, Sn, Sb, Pt, Ni, Fe, Co, Cr, V, Cu, Mn, Pb, their oxides, borides, nitrides, and carbides, as well as C and B4C, and compounds of said materials. For example, some of these materials are identified in DE 10 2017 200667A1 as materials for a braking layer system designed to counteract hydrogen atom penetration into the mirror substrate. The choice of material depends on the crystal structure: for example, close packing is advantageous, as is present in the case of Al, Au, Ag, and Zn. Certain materials, such as Mo, Si, C, and B4C, are commonly used in EUV lithography units.

[0025] In another embodiment, the hydrogen barrier forms a coating that at least partially, and particularly completely, covers the hydrogen-sensitive material. The coating may comprise a single layer or may be formed by stacking multiple layers on top of each other. The coating is preferably applied directly to the hydrogen-sensitive material on the back side of the substrate, i.e., particularly actuators, adhesive layers, insulating layers, conductor cables, or conductor tracks, etc., which are formed of materials that degrade upon contact with hydrogen.

[0026] The coating, or at least one layer of coating, preferably comprises a material having the properties described above regarding the hydrogen diffusion coefficient and the solubility of hydrogen. The material discussed may in particular be one of the materials described earlier above. Typically, at least one layer comprises or is composed of a material whose solubility in hydrogen is lower than that of the hydrogen-sensitive material to be protected.

[0027] The materials previously mentioned above, along with other materials, for coatings and hydrogen barrier layers can be applied to the back side of a substrate and / or components provided therein by various coating methods. Materials can be deposited from vapor phases, for example by physical vapor deposition (PVD), particularly by plasma-enhanced PVD; by chemical vapor deposition (CVD), particularly by plasma-enhanced CVD (PECVD); by atomic layer deposition (ALD), particularly by plasma-enhanced ALD; by sputtering, particularly magnetron sputtering, etc. In particular, sputtering and electron beam evaporation have proven advantageous for the application of metallic layers.

[0028] For the purpose of achieving a good barrier effect, it is generally advantageous if the material of the hydrogen barrier layer is applied such that the layer exhibits the maximum density and has as few pinholes as possible, through which hydrogen can permeate into the underlying material.

[0029] Hydrogen barriers are preferably configured as coatings in the form of a multilayer system of barrier layers with different materials, for example, as described in DE 10 2017 200 667 A1, the entire contents of which form part of the content of this application by reference. For example, in the case of a two-layer system, i.e., in the case of a coating comprising a pair of layers, pinholes or defects in a single layer will not be perpetuated as pinholes or defects in subsequent single layers. Therefore, in the coating, it is preferable to apply different materials from those already determined above in a modified manner, i.e., as two layers. Particularly preferably, multiple two layers are applied. The materials discussed can be, for example, alternately applied nitrides and carbides, particularly MAX phases, which are layered hexagonal nitrides and carbides. It should be understood that three or more of the above-described materials can also be used in coatings in the form of a multilayer system.

[0030] In one development example, the coating includes at least one hydrogen barrier layer applied over another layer. In this case, the coating comprises a combination of a thick capping layer and a hydrogen barrier layer made of a material with high barrier effect. Other layers located below the hydrogen barrier layer and covering the hydrogen-sensitive material here function to compensate for irregularities in the substrate and provide better growth conditions for the hydrogen barrier layer. For example, the capping layer may include SiO2. The capping layer is typically over 100 nm thick; the hydrogen barrier layer is typically thinner than 100 nm. In such a coating, multiple bilayers of capping and hydrogen barrier layers can also be combined. It should also be understood that a multilayer or bilayer system of multiple hydrogen barrier layers can also be located on the capping layer.

[0031] In another embodiment, the hydrogen barrier includes a protective film that at least partially, and particularly completely, covers the hydrogen-sensitive material. The protective film is typically adhered to the hydrogen-sensitive material. The protective film does not necessarily need to be in contact with the material to be protected or its surface in every location; in other words, gaps may form between the protective film and the hydrogen-sensitive material, at least in sub-regions. However, it has proven advantageous to apply the protective film over the entire area of ​​the back side of the substrate or to the material / part to be protected on the back side of the substrate. As mentioned above, if the protective film is formed of or contains a material having a low hydrogen diffusion coefficient and / or low solubility for hydrogen, the protective film itself can serve as a hydrogen barrier. Such a material may optionally be formed on the surface of the protective film facing or away from the surrounding environment.

[0032] In another embodiment, the protective film has at least one hydrogen barrier layer on its surface facing the surrounding environment and / or on its surface facing away from the surrounding environment. The hydrogen barrier layer may include, for example, a metal layer, particularly an aluminum layer or an aluminum oxide layer. If the material is hydrogen-sensitive, the hydrogen barrier layer applied to the surface of the protective film facing the surrounding environment can also provide protection against hydrogen attack on the material of the underlying protective film. If the protective film itself is hydrogen-resistant, the hydrogen barrier layer can also be mounted on the surface of the protective film facing away from the surrounding environment. In this way, water can be kept away from the hydrogen barrier layer.

[0033] As mentioned above, the adhesive layer can be applied with an uneven thickness, meaning it protrudes only slightly or not at all into the gap between the actuators. If the protective film adheres to the top side of the actuator, i.e., the side facing away from the substrate, the protective film can, in principle, extend in a planar manner without extending downward into the gap between the actuators and without contacting the surface of the adhesive layer.

[0034] In one embodiment, the protective film protrudes into the corresponding gap between the sides of the actuator and covers a preferred cavity or groove-shaped recess in the adhesive layer. It is generally advantageous that the protective film protrudes into the corresponding gap and contacts or connects to the adhesive layer. In the simplest case, the connection can be created by adhering the protective film to the adhesive layer before it is fully dry, or if the protective film itself is self-adhesive. Where the adhesive layer partially protrudes upward into the gap between the actuators, the protective film can be connected to the adhesive layer over the entire area by pressing, for example, forming a cavity or groove-shaped recess in the adhesive layer. In this case, the adhesive layer may optionally protrude upward into the gap at least on the actuator, and the thickness of the entire adhesive layer may optionally be greater than the height of the actuator, meaning that the adhesive layer not only protrudes into the gap (except for the cavity or groove-shaped recess) but also protrudes entirely on the actuator. If the adhesive layer does not protrude or only partially protrudes into the gap, the protective film may optionally be directly fixed, particularly glued, to the side of the actuator. The protective film is typically formed of a flexible material and may comprise multiple layers.

[0035] In principle, additional adhesion promoter layers or other functional layers can be applied at each interface on the back side of the substrate, for example, on the coating or protective film. For example, (other) protective layers can be applied that protect the material on the back side of the substrate from other contaminants (and optionally, additionally, from hydrogen). Such layers can be integrated into or applied to the coatings or protective films described earlier above.

[0036] In another embodiment, the actuator is configured as a piezoelectric actuator or an electrostrictive actuator. A piezoelectric actuator or electrostrictive actuator, i.e., an actuator comprising at least one electrostrictive material, can produce very small deformations in the substrate in a targeted manner. The piezoelectric actuator or electrostrictive actuator can, for example, be a linear actuation motor that applies substantially point-to-point force to the substrate. It should be understood that other types of actuators can be used instead of piezoelectric actuators or electrostrictive actuators. The actuators can be arranged in a grid pattern on the back side of the substrate. Associated insulating layers, conductor cables, and conductor tracks are also mounted on the back side of the substrate and can be protected by hydrogen barriers.

[0037] Other aspects of the invention relate to an optical arrangement, and more particularly to an EUV lithography apparatus comprising at least one mirror arrangement as described above. For the purposes of this application, a lithography apparatus is considered to be an (optical) device that can be used in the field of lithography. In addition to a lithography unit for manufacturing semiconductor components, the apparatus may be, for example, an inspection system for inspecting photomasks (hereinafter also referred to as mask masters) used in a lithography unit to inspect a semiconductor substrate (hereinafter also referred to as a wafer) to be structured, or a metrology system for measuring a lithography unit or its components, such as measuring a projection system.

[0038] Optical arrangements or lithography equipment may be, in particular, EUV lithography equipment configured for use radiation at wavelengths in the EUV wavelength range of about 5 nm to about 30 nm, or DUV lithography equipment configured for use radiation in the DUV wavelength range of about 30 nm to about 370 nm. The optical elements or mirror arrangements of EUV lithography equipment typically operate in a vacuum environment.

[0039] Referring to the accompanying drawings, which illustrate essential details of the invention, other features and advantages of the invention will become apparent from the following description of exemplary embodiments and from the claims. Individual features may be implemented individually or as a plurality of desired combinations in any variation of the invention. Attached Figure Description

[0040] Exemplary embodiments are illustrated in the schematic drawings and explained in the following description. In the drawings:

[0041] Figure 1 A schematic diagram of an EUV lithography unit with multiple actuators for aberration correction is shown.

[0042] Figure 2 It shows having Figure 1 A schematic cross-sectional view of the arrangement of the reflectors and the reflectors having an adhesive layer for fixing the actuator to the substrate;

[0043] Figure 3 It shows Figure 2 A schematic diagram showing the details of the mirror arrangement, wherein the adhesive layer protrudes from the actuators, and recesses are formed between the actuators, the recesses being covered by a hydrogen protective film; and

[0044] Figure 4a b shows something similar to Figure 3 The schematic diagram shows the application of a coating to one surface of the adhesive layer and to the actuator, the coating forming a hydrogen barrier.

[0045] In the following description of the accompanying drawings, the same reference numerals are used for the same or functionally identical parts.

[0046] Figure 1 The structure of an apparatus for EUV lithography, specifically a so-called wafer scanner, is schematically shown in the form of an EUV lithography unit 1. The EUV lithography unit 1 includes an EUV light source 2 for generating EUV radiation with high energy density in the EUV wavelength range below 50 nanometers, particularly between about 5 nanometers and about 15 nanometers. The EUV light source 2 can, for example, be configured as a plasma light source for generating laser-induced plasma. Figure 1 The EUV lithography unit 1 shown is designed for an operating wavelength of 13.5 nm EUV radiation. However, the EUV lithography unit 1 can also be configured for different operating wavelengths within the EUV wavelength range, such as 6.8 nm.

[0047] The EUV lithography unit 1 also includes a light-collecting reflector 3 to focus the EUV radiation from the EUV light source 2 to form an illumination beam 4 and to further increase the energy density in this way. The illumination beam 4 is used to illuminate the structured object M through an illumination system 10, which in this example has five reflective optical elements 12 to 16 (reflectors).

[0048] The structured object M can be, for example, a reflective photomask having reflective and non-reflective regions, or at least fewer reflective regions, for creating at least one structure on the object M. Alternatively, the structured object M can be a plurality of micromirrors arranged in a one-dimensional or multi-dimensional configuration and optionally movable about at least one axis to set the angle of incidence of EUV radiation on the respective mirrors.

[0049] The structured object M reflects a portion of the illumination beam 4 and shapes the projection beam 5, which carries information about the structure of the structured object M, and is irradiated into the projection lens 20, which produces an image of the structured object M or its corresponding sub-regions on the substrate W. The substrate W (e.g., a wafer) comprises a semiconductor material (e.g., silicon) and is mounted on a mount also known as a wafer stage WS.

[0050] In this example, the projection lens 20 has six reflective optical elements 21 to 26 (mirrors) to produce an image of the structure present at the structured object M on the wafer W. The number of mirrors in the projection lens 20 is typically between four and eight; however, two mirrors may also be used if appropriate.

[0051] In addition to the reflective optical elements 3, 12 to 16, 21 to 26, the EUV lithography unit 1 also includes non-optical components, such as carrier structures, sensors, actuators, etc., for the reflective optical elements 3, 12 to 16, 21 to 26. Figure 1 A plurality of actuators 27 are schematically shown mounted on the back of the sixth reflector 26 of the projection lens 20 to perform targeted deformation of the lens and, in the process, compensate for aberrations that occur when the structure is imaged onto the wafer W through the projection lens 20. To drive the actuators 27 in a targeted manner, the EUV lithography unit 1 includes a control device 28 (e.g., in the form of a control computer) that communicates with the actuators 27 via signal lines (not shown).

[0052] Figure 2 The detailed diagram shows part of the corresponding mirror arrangement 30. Figure 1 The reflector 26. The reflector arrangement 30 (more specifically, reflector 26) includes a substrate 31, which in the illustrated example is formed of fused silica or titanium-doped fused silica (ULE). Different materials with low coefficients of thermal expansion or very low dependence of their coefficients of thermal expansion on temperature, such as certain glass ceramics, can also be used as substrate materials. Applied to the front surface 31a of the substrate 31 of the reflector 26 is a reflective coating 32, which is configured such that, for a specific range of incident angles, the incident EUV radiation 5 is reflected with relatively high reflectivity in a narrow spectral range near the operating wavelength of 13.5 nm. The reflective coating 32 is configured such that it acts as an interference layer system for reflecting EUV radiation 5. The reflective coating 32 alternately comprises a first layer of a first layer material in the form of silicon and a second layer of a second layer material in the form of molybdenum. Different first and second layer materials (e.g., in the form of molybdenum and beryllium) are also possible depending on the operating wavelength.

[0053] The actuator 27 serves the targeted localized deformation of the reflective mirror surface 32a formed on the reflective coating 32. Figure 2 In the example shown, it is configured as a piezoelectric actuator or an electrostrictive actuator. Actuator 27 is fixed to the back surface 31b of substrate 31 by an adhesive layer 33. The adhesive layer 33 can be applied directly to the back surface 31b of substrate 31, but in the example shown, an intermediate layer 34 is applied to the back surface 31b of substrate 31, and the adhesive layer 33 is applied to the intermediate layer 34. The material of the intermediate layer 34 can include, for example, Cr, V, Si, Al, Ta, Ti, Ru, Cu, Al₂O₃, Ta₂O₅, TiO₂, chromium oxide, vanadium oxide, La₂O₃, ZrO₂, etc.

[0054] In the example shown, the adhesive layer 33 has a constant thickness D and is applied to a region on the back side 31b of the substrate 31. The actuator 27 is mounted or embedded in the adhesive layer 33 and protrudes from it. The actuators 27 are glued together at a distance from each other in a two-dimensional grid on the back side 31b of the substrate 31. For simplicity, Figure 2Only two directly adjacent actuators 27 are shown, with a gap 35 between them. It should be understood that a large number of actuators 27 are typically present in the grid, with pairs of adjacent actuators 27 separated from each other by gaps 35. The gaps 35 between the actuators 27 typically have the same width; in other words, the actuators 27 are uniformly distributed on the back surface 31b of the substrate 31. One or more actuators 27 may also form assemblies with gaps or openings 35, or multiple actuator assemblies may be applied to the back surface 31a of the substrate 31. A single actuator or actuator assembly 27 may optionally be applied to the back surface 31b of the substrate 31.

[0055] The adhesive layer 33 extends not only below the actuator 27 or between the actuator 27 and the back surface 31b of the substrate 31, but also into the corresponding gap 35 between two adjacent actuators 27. Figure 2 In the example shown, the thickness D of the adhesive layer 33 is selected such that the adhesive layer 33 does not protrude into the gap 35, but is flush with the bottom side of the actuator 27 in the surface regions 33a-c exposed to the surrounding environment. Alternatively, the thickness D of the adhesive layer 33 can be selected such that the gap 35 is wholly or partially filled by the adhesive layer 33. The thickness D of the adhesive layer 33 can also be specifically selected to have dimensions such that the adhesive layer 33 covers the top side of the actuator 27. The adhesive layer 33 can also be thinner or have an irregular thickness.

[0056] Figure 1 The reflective optical elements 3, 12 to 16 of the illumination system 10 and the reflective optical elements 21 to 26 of the projection lens 20 in the EUV lithography unit 1 are arranged in a vacuum environment with a residual gas atmosphere. Hydrogen 37 is present in the environment 36 surrounding the mirror arrangement 30 and therefore also in the environment surrounding the adhesive layer 33, at least during cleaning cycles. Hydrogen 37 may exist in different excited states, such as molecular hydrogen (H2), hydrogen-excited molecular or atomic hydrogen, hydrogen ions, etc.

[0057] Components mounted on the back surface 31b of substrate 31, particularly actuator 27, typically have a hydrogen-sensitive material M, i.e., a material that degrades upon contact with hydrogen 37 on its environment-facing surface 36. The hydrogen-sensitive material M can be, for example, the material of the actuator 27's housing, and can also be conductor tracks, conductor cables, insulating layers, etc., applied to actuator 27 and optionally to intermediate layer 34. Conductor tracks and insulating layers are typically made of plastic materials that have high solubility for hydrogen 37 and degrade upon chemical reaction with hydrogen. The material of adhesive layer 33 and, where appropriate, the material of substrate 31 are also typically not chemically inert to the attack of hydrogen 37.

[0058] To protect the hydrogen-sensitive material M on the back surface 31a of the substrate 31 from hydrogen 37 from the surrounding environment 36 of the mirror arrangement 30, the mirror arrangement 30 has a hydrogen barrier 38, which can be configured in various ways, as shown in the following reference. Figure 3 and Figure 4a b. More detailed description. Figure 3 and Figure 4a b shows only the details of the mirror arrangement 30 or the hydrogen barrier 38, but it generally extends over the entire back surface 31a of the substrate 31.

[0059] The hydrogen barrier 38, described in more detail below, can also be used as a water vapor diffusion barrier to protect the adhesive layer 33 from the penetration or inward diffusion of water vapor 39 (see below). Figure 2 If the concentration of water vapor 39 in the surrounding environment 36 of the mirror arrangement 30 changes, the diffusion of water vapor 39 into or out of the adhesive layer 33 becomes a particular problem, because the expansion or contraction of the adhesive in the adhesive layer 33 depends on the amount of water vapor 39 absorbed, causing stress in the adhesive layer 33 to be transferred to the substrate 31 and potentially leading to undesirable deformation at the mirror surface 32a. The same applies to other organic materials mechanically attached to the mirror.

[0060] Figure 3 The hydrogen barrier 38 shown includes a protective film 40 made of a flexible film material. Applied to the protective film 40, on the top side 40a facing away from the substrate 31, is a hydrogen barrier layer 41, which in the illustrated example is composed of Al. Aluminum has a density of less than approximately 5 x 10⁻⁶. -14 m 2 The low hydrogen diffusion coefficient DW is also present. Furthermore, aluminum is a chemically inert material, and its solubility for hydrogen 37 is lower than that of the material in the adhesive layer 33.

[0061] Different materials have low hydrogen diffusion coefficients (DW), for example, less than 5 x 10⁻⁶. -14 m 2 / s, preferably less than 1x10 -17 m 2 / s, especially less than 1x10 -21 m 2A hydrogen barrier layer 41 can be applied to the protective film 40, such as Au, Ag, Zn, Mo, Si, W, Ti, Sn, Sb, Pt, Ni, Fe, Co, Cr, V, Cu, Mn, Pb, their oxides, borides, nitrides and carbides, C, B4C and their compounds. The hydrogen barrier layer 41 may also comprise at least one metal oxide or be composed of a metal oxide. In particular, the metal oxide has a high (negative) enthalpy of formation, less than about -300 kJ / mol O2, preferably less than -800 kJ / mol O2, more preferably less than -1000 kJ / mol O2, and is generally inert to chemical reactions with hydrogen 37. In particular, Al2O3, MgO, CaO, La2O3, TiO2, ZrO2, Ta2O5, Y2O3, Ce2O3 and their compounds have proven to be advantageous materials for the hydrogen barrier layer 41. The same applies to nitrides. For example, the formation free enthalpy of metal nitrides is less than -200 kJ / mol N2, preferably less than -350 kJ / mol N2, and more preferably less than -600 kJ / mol N2. These nitrides are generally inert to chemical reactions with hydrogen 37, and therefore can be used as materials for hydrogen barrier layer 41.

[0062] exist Figure 3 In the example shown, the protective film 40 adheres to the entire area of ​​the top side 33a of the adhesive layer 33. In this case, the adhesive layer 33 protrudes upward from the top side of the actuator 27. Between multiple pairs of adjacent actuators 27, the protective film 40 protrudes into the gap 35, meaning it extends downward from the top side of the two actuators 27 in the direction of the back surface 31a of the substrate 31. Figure 3 In the example shown, the protective film 40 covers the cavity-like recesses 42 in the adhesive layer 33. Figure 3 In the example shown, the recess 42 extends within the gap 35 to an approximately horizontal plane on the bottom side of the actuator 27. The recess 42 reduces the volume of the adhesive located within the gap 35. This helps to reduce stress in the adhesive layer 33 when absorbing / releasing water vapor 39, and in this way, reduces stress in the substrate 31.

[0063] exist Figure 3 In the example shown, the membrane 40 is not directly connected to the actuator 27, but only to the surface 33a of the adhesive layer 33. Therefore, in the event of adhesive drift, the opposing sides of the protective membrane 40 can move toward or away from each other in the area of ​​the cavity or groove 42 to counteract the stress occurring in the adhesive layer 33.

[0064] In the illustrated example, the protective film 40 forms a water vapor diffusion barrier, meaning it is composed of or includes a material that prevents or counteracts the penetration of water vapor 39 into the adhesive layer 33. For this purpose, the protective film 40 is formed of or includes a material with low water diffusivity. The protective film 40 can be a two-layer film, for example, having a first layer of Al2O3 as a material with low water diffusivity, which acts as a water vapor diffusion barrier and is applied to a second layer, such as a self-adhesive layer. Alternatively or additionally, the protective film 40 can have a hydrophobic surface 40a, which can be produced, for example, by plasma treatment or termination. The surface 41a of the water vapor barrier layer 41 (e.g., with Al as the layer material) can also be made hydrophobic by suitable surface treatment. Where the water vapor diffusion barrier in the form of the protective film 40 is itself insensitive to hydrogen, the switching sequence can be advantageous, such that the hydrogen barrier layer 41 is applied to the bottom side 40b of the protective film 40 facing the substrate 31. A corresponding hydrogen barrier layer 41 can also be applied to the top side 40a and bottom side 40b of the protective film 40.

[0065] Figure 4a Figure 3b shows a hydrogen barrier in the form of a coating 38, which is applied to the back surface 31b of the substrate 31 and to components provided there there, in other words, specifically to the actuator 27 and the adhesive layer 33. Figure 4a In the example shown, coating 38 consists of a single hydrogen barrier layer 44, which is applied not only to the top side of actuator 27 but also to the sidewalls of actuator 27 and the top side of adhesive layer 33 within the corresponding voids 35. In the example shown, hydrogen barrier layer 44 is formed of Al2O3, but may also comprise one or more of the materials described earlier above, or different materials, which firstly have a low hydrogen diffusion coefficient DW and secondly have low solubility for hydrogen 37.

[0066] Figure 4b A hydrogen barrier 38 in the form of a coating is shown, which also completely covers the hydrogen-sensitive material M on the back side 31b of the substrate 31. (Compared to...) Figure 4a Compared to the coating 38 shown, Figure 4b The coating 38 shown has a relatively thin hydrogen barrier layer 44, which is applied over another relatively thick capping layer 43. The layer 43, covering the hydrogen-sensitive material M, compensates for irregularities and provides better growth conditions for the hydrogen barrier layer 44. In the example shown, SiO2 is present in the capping layer 43. The thickness of the capping layer 43 is typically greater than 100 nm; the thickness of the hydrogen barrier layer 44 is typically less than 100 nm. Figure 4b Compared to the contents shown, the hydrogen barrier 38 may include multiple double layers, each double layer consisting of a cover layer 43 and a hydrogen barrier layer 44 applied thereto.

[0067] The hydrogen barrier layer 44 may be formed from one or more of the materials described earlier above. The hydrogen barrier layer 44 may also include a hydrophobic material, or its surface 44a may have hydrophobic properties to serve as a water vapor diffusion barrier.

[0068] Replacement Figure 3 and Figure 4a The individual hydrogen barrier layers 41 and 44 shown in Figures 4 and 5, and the hydrogen barrier element 38 can be configured as a coating having two or more hydrogen barrier layers applied overlapping each other. In this way, for example in the case of a bilayer system, i.e., a coating 38 comprising a pair of hydrogen barrier layers, pinholes or defects in a single layer will not continue to be pinholes or defects in subsequent single layers. Therefore, in this type of coating 38, it is preferable to alternately apply different materials from the materials previously identified above, i.e., as bilayers. It is advantageous to apply two or more such bilayers overlapping each other. The materials of the hydrogen barrier layers can be, for example, alternately applied nitrides and carbides, particularly the MAX phase, i.e., layered hexagonal nitrides and carbides. It should be understood that three or more of the above-mentioned materials can also be used in the coating 38 in the form of a multilayer system.

[0069] The coating 38 (particularly the hydrogen barrier layer 44) can be applied to the surface 33a of the adhesive layer 33 and the actuator 27 in various ways, for example, by vapor deposition, i.e., by PVD, CVD, such as by plasma-enhanced CVD or PVD, by ALD, particularly by plasma-enhanced ALD, by sputtering, particularly by magnetron sputtering, by electron beam evaporation, etc. The operating parameters when applying the coating 38 or the hydrogen barrier layer 44 are typically selected so that it can be deposited at a high density and with as few pinholes as possible.

[0070] Figure 3 The hydrogen barrier 38 shown can optionally be coupled with Figure 4a The hydrogen barrier 38 of substrate 31 and substrate 31b are combined together. This combination is achieved by covering a portion or sub-region of the back surface 31b of substrate 31 with the hydrogen barrier 38 in the form of a protective film 40 (coated with a hydrogen barrier layer 41), and using the hydrogen barrier 38 according to the requirements of substrate 31b. Figure 4a Hydrogen barrier 38 in the form of a coating covers other portions or sub-regions on the back side 31b of substrate 31. In the event that a hydrogen-insensitive material is applied to the back side 31b of substrate 31, the hydrogen barrier 38 provided on the back side 31b of substrate 31 may optionally be omitted in the areas where such material is provided.

Claims

1. A mirror arrangement (30), comprising: A substrate (31) having a front side (31a) and a back side (31b), the front side (31a) having a reflective mirror (32a) for reflecting radiation (5) and the back side (31b) facing away from the front side (31a), and At least one actuator (27) is used to generate deformation of the reflective mirror surface (32a). Its features are, The at least one actuator (27) is fixed to the back side (31b) of the substrate (31), and the mirror arrangement (30) has a hydrogen barrier (38) configured to protect the hydrogen-sensitive material (M) on the back side (31b) of the substrate (31) from hydrogen (37) from the surrounding environment (36) of the mirror arrangement (30), wherein the at least one actuator (27) is fixed to the back side (31a) of the substrate (31) by an adhesive layer (33). Wherein, the surfaces (41a, 44a) of the hydrogen barrier (38) facing the surrounding environment (36) are hydrophobic and / or the hydrogen barrier (38) comprises at least one hydrophobic material, and The exposed surface areas (33a-c) of the continuous adhesive layer (33) formed in the gap between the actuators are protected from hydrogen (37) by the hydrogen barrier (38).

2. The mirror arrangement according to claim 1, wherein, The hydrogen-sensitive material (M) is on at least one actuator (27).

3. The mirror arrangement according to claim 1, wherein, The hydrogen barrier (38) forms a water vapor diffusion barrier to protect the adhesive layer (33) from water vapor (39).

4. The mirror arrangement according to any one of the preceding claims, wherein, The hydrogen diffusion coefficient (DW) of the hydrogen barrier (38) is less than 5 × 10⁻⁶. -14 m 2 / s.

5. The mirror arrangement according to claim 4, wherein, The hydrogen diffusion coefficient (DW) is less than 1 × 10⁻⁶. -17 m 2 / s.

6. The mirror arrangement according to claim 4, wherein, The hydrogen diffusion coefficient (DW) is less than 1 × 10⁻⁶. -21 m 2 / s.

7. The mirror arrangement according to any one of the preceding claims, wherein, The hydrogen barrier (38) comprises at least one material and / or a combination of materials having a lower solubility for hydrogen (37) than the hydrogen-sensitive material (M).

8. The mirror arrangement according to any one of the preceding claims, wherein, The hydrogen barrier (38) comprises at least one material in the form of an oxygen-containing compound having a formation free enthalpy of less than -400 kJ / mol O2.

9. The mirror arrangement according to claim 8, wherein, The free enthalpy of formation of this oxygen-containing compound is less than -800 kJ / mol O2.

10. The mirror arrangement according to claim 8, wherein, The free enthalpy of formation of this oxygen-containing compound is less than -1000 kJ / mol O2.

11. The mirror arrangement according to any one of the preceding claims, wherein, The hydrogen barrier (38) comprises at least one material in the form of a nitrogen-containing compound having a formation free enthalpy of less than -200 kJ / mol N2.

12. The mirror arrangement according to claim 11, wherein, The free enthalpy of formation of this nitrogen-containing compound is less than -350 kJ / mol N2.

13. The mirror arrangement according to claim 11, wherein, The free enthalpy of formation of this nitrogen-containing compound is less than -600 kJ / mol N2.

14. The mirror arrangement according to any one of the preceding claims, wherein, The hydrogen barrier (38) comprises at least one metal oxide.

15. The mirror arrangement according to claim 14, wherein, The metal oxide is selected from the group consisting of Al2O3, MgO, CaO, La2O3, TiO2, ZrO2, Ta2O5, Y2O3, Ce2O3 and their compounds.

16. The mirror arrangement according to any one of the preceding claims, wherein, The hydrogen barrier (38) comprises at least one material selected from the group consisting of Al, Au, Ag, Zn, Mo, Si, W, Ti, Sn, Sb, Pt, Ni, Fe, Co, Cr, V, Cu, Mn, Pb, their oxides, borides, nitrides and carbides, as well as C and B4C.

17. The mirror arrangement according to any one of the preceding claims, wherein, The hydrogen barrier has a coating or forms a coating (38) that at least partially covers the hydrogen-sensitive material (M).

18. The mirror arrangement according to claim 17, wherein, The coating (38) completely covers the hydrogen-sensitive material (M).

19. The mirror arrangement according to claim 17, wherein, The coating (38) includes at least one hydrogen barrier layer (44).

20. The mirror arrangement according to claim 19, wherein, The at least one hydrogen barrier layer (44) is applied on the other layers (43).

21. The mirror arrangement according to any one of the preceding claims, wherein, The hydrogen barrier (38) has a protective film (40) or forms a protective film (40) that at least partially covers the hydrogen-sensitive material (M).

22. The mirror arrangement according to claim 21, wherein, The protective film (40) completely covers the hydrogen-sensitive material (M).

23. The mirror arrangement according to claim 21, wherein, The protective film (40) has at least one hydrogen barrier layer (41) on its surface (40a) facing the surrounding environment and / or on its surface (40b) facing away from the surrounding environment.

24. The mirror arrangement according to claim 21, wherein, The protective film (40) protrudes into the corresponding gap (35) between adjacent actuators (27) and covers the recess (42) in the adhesive layer (33).

25. The mirror arrangement according to claim 24, wherein, The recess (42) is cavity-shaped or groove-shaped.

26. The mirror arrangement according to any one of the preceding claims, wherein, The actuator (27) is configured as a piezoelectric actuator or an electrostrictive actuator.

27. An optical arrangement comprising: At least one mirror arrangement (30) as described in any of the preceding claims.

28. The optical arrangement according to claim 27, wherein, The optical arrangement is an EUV lithography device (1).

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